Control apparatus



Nov. 21, 1950 R. F. WILD ,530,928 coN'rRL APPARATUS ed Oct. 6. 1945 4Sheet -s 1 FIG.I

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INVENTOR. DOLF F. WILD ATTORNE Nov. 21, 1950 R. F. WILD CONTROLAPPARATUS Filed Oct. 6, 1945 4 Sheets-Sheet 2 FIG.2

INVENTOR. RUDOLF F. WILD 1 ATTORNEY.

Nov. 21, 1950 R. F. WILD 2,530,928

CONTROL APPARATUS Filed Oct. 6, 1945 4 Sheets-Sheet 5 FIG. 3

FREQUENCY HIGH FREQUENCY LOW g, OSCILLATOR u snsmu. E O

OSCILLATOR l2 S|GNAL INPUT TO RECEIVER (0 INPUT TO RECEIVER VOLTAGE AAAAA AML VV\ VV\ VV\ m INPUT TO DISCRIMINATOR w INPUT TO mscmumxron r I Fi TIME J I J T J m DISCRIMINATOR OUTPUT' (c DISCRIMINATOR OUTPUT 9 LTIME TIME I (chA-C COMPONENT OF (am-c COMPONENT OF plscmmmnon OUTPUTmscmmmnoa OUTPUT INVENTOR.

RUDOLF F. WILD Mam ATTORNEY.

Nov. 21, 1950 R. F. WILD 2,530,928

CONTROL APPARATUS Filed Oct. 6, 1945 4 Sheets-Sheet 4 POWER SUPPLY nov.,6on1- FIG. 4 c i INVENTOR. RUDOLF F. WILD A fiiwm AT TO R NEY.

Patented Nov. 21, 1950 CONTROL APPARATUS Rudolf F. Wild, Philadelphia,Pa., assignor, by mesne assignments, to Minneapolis-Honeywell RegulatorCompany, Minneapolis, Minn., a corporation of Delaware ApplicationOctober 6, 1945, Serial No. 620,832

4 Claims. 1

The present invention relates to improvements in telautograph systems.

An object of the invention is to provide improved apparatus fortransmitting plotted data or written information from a transmittingstation to one or more receiving stations which may be remotely locatedwith respect to each other as well as with respect to the transmittingsta- Another object of the invention is to provide such a telautographsystem which is rapid in operation and accurate in the reproduction ofthe transmitted material.

A further object of the invention is the provision in the telautographsystemof the type referred to above of simple and eificient switchingmeans to permit the use of a plurality of receiving stations with eachtransmitting station.

A still further object of the invention is to provide a telautographsystem in which any receiver or receivers in the system may be placed inor removed from operation without afiecting in any way the operation ofthe remainder of the system. To the attainment of this end suitablemeans are provided according to the invention for substituting a dummyload for each of the receivers which is removed from operation.

Another object of the invention is to provide such a telautograph systemin which the plotting coordinates at the transmitting and receivingstations may be either circular or rectangular, as desired.

A further object of the invention is to provide a telautograph systemadapted to be arranged to selectively transmit plotted data or writteninformation from a plurality of transmitting stations to one or more ofa plurality of receiving stations.

A more specific object of the invention is to provide an improvedelectrical telautograph system in which suitable means are incorporatedin the transmitter to translate the movements of a stylus in one or theother of two coordinates into a corresponding shift in frequency of anassociated one of two oscillating signals, and in which suitable meansare provided in each of the receivers for detecting such shifts infrequency of the two oscillating signals for imparting to a movablereceiver element movements corresponding to the movements of thetransmitter stylus.

It is also a specific object of the invention to provide an electricaltelautograph system in which the transmitter incorporates an amplifyingdevice having an output circuit adapted to be c cte to each o thevarious receivers by means of an associated transmission line or cableterminated in its characteristic impedance and including two conductorsover which both of the oscillating signals are transmitted, whichamplifying device includes a cathode follower circuit for matching theimpedance of said output circuit to the characteristic impedance of thetransmission line for maximum transfer of energy from the transmitter toeach of the receivers.

Another specific object of the invention is to provide in such anelectrical telautograph system suitable electrical devices for providingthe required zero and span adjustments.

In accordance with the present invention the position of a point to betransmitted is considered in terms of its location with-respect toselected coordinates. For example when rectangular coordinates areutilized, the position of a point to be-transmitted is considered interms the distance between said point and each of two mutuallyperpendicular lines or coordinate axes. .It will be apparent that if thedistance from the point to each of the lines is measured, the positionof the point may be readily determined. Accordingly, if the magnitude ofthe deviation in position of the point from each of the coordinate axesis transmitted to a remotely located station, the two deviations can becombined at that remote station to there cause an element to assume acorresponding position relative to similar coordinate axes located atthat station.

Specifically, suitable means are provided at the transmitting stationfor creating two oscillating Signals, each of variable frequencydetermined by the magnitude of the deviation in position of the pointfrom an associated one of the coordinate axes. These two oscillatingsignals are conducted by means of a single transmission line or cable tothe receiving station in which suitable frequency responsive means areprovided for determining the frequency of each of the receivedoscillating signals and for actuating a movable receiver element to apositionrelative to two ing means to permit one or more of the receiversto be placed in or removed from operation as desired. An importantfeature of the invention resides in the fact that any receiver orreceivers in the system may be placed in or removed from operationwithout affecting in any way the operation of the remainder of thesystem.

The various features of novelty which characterize this invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,however, its advantages and specific objects obtained with its use,reference should be had to the accompanying drawings and descriptivematter in which is illustrated and described a preferred embodiment ofthe invention.

In the drawings:

Fig. 1 illustrates a wiring diagram of the transmltter mechanism of apreferred embodiment of the invention;

Fig. 2 illustrates a wiring diagram of a preferred form of receivermechanism which may be employed in conjunction with the transmittingmechanism of Fig. 1;

Fig. 3 shows voltage diagrams illustrating the operation of thetransmitting and receiving mechanism of Figs. 1 and 2; and

Fig. 4 is a wiring diagram showing switching mechanism which may beutilized for connecting the transmitting mechanism of Fig. 1 to one ormore of a plurality of receiving mechanisms of the form shown in Fig. 2.

In Fig. 1 there is illustrated a transmitter embodying the principles ofmy invention for producing two separate variable frequency highfrequency oscillating currents, each corresponding in frequency to thedeviation of a marking element I from two mutually perpendicular linesor coordinate axes which have been designated by the referencecharacters 2 and 3, respectively, and are drawn on a plotting board ortable 4. The marking element I may comprise either a pen or a pencil andfor purposes of illustration will be considered to be a pencil.

Data is plotted on the plotting board 4 with the pencil I, the latterbeing suspended from a socalled transmitting head indicated generally bythe reference character 5. The transmitting head 5 has been shown invery diagrammatic manner in Fig. l inasmuch as the details of thatdevice comprise no part of the present invention, but are the inventionof George W. Barnes, Jr., John F. Goetz, and Walter P. Wills and aredisclosed in an application, Ser. No. 620,827 filed concurrentlyherewith, which issued as Patent No. 2,508,592 on May 23, 1950. Awriting handle is preferably attached to the holder 6 for the pencilto.faci1itate the plotting of information to be transmitted on theplotting board 4. The pencil, when not in use, is automatically liftedfrom the plotting board 4 by spring means located within the holder 6and disclosed in detail in the Barnes, Goetz and Wills patent. A switch1 is provided in the pencil holder 6 for actuation by writing pressureof the pencil on the plotting board for the purpose of actuating asolenoid at the remotely located receiver shown in Fig. 2 so that themarking element at the receiver is adapted to engage the recording chartonly when the transmitter pencil is in contact with the plotting board.A knurled nut 8 at the top of the pencil holder is provided to permitthe latter to be turned, whereby plotting can be done from any side ofthe plotting board. After the pencil 4 holder has been adjusted to adesired position, the knurled nut should be tightened.

The transmitting head includes certain of the electrical components ofthe transmitting mechanism and in particular houses variable electricalcondensers 9 and I 0, and also includes suitable cams and gimbal jointsso that the condenser 9 is arranged to be varied in capacity inaccordance with the movements of the pencil I along one coordinate, forexample, along the coordinate 2, while the condenser I0 is arranged tobe varied in capacity in accordance with the movements of pencil I inthe other coordinate. The cams referred to serve a compensating purposerequired because the angle of the deflection of the holder 6 is notdirectly proportional to the linear movement of the pencil I along theplotting board. The transmitter head also includes two electricaloscillation circuits II .and I2, respectively associated with condensers9 and ID.

Oscillation circuits II and I2 may be and are shown as being identicalto each other, and therefore, only oscillation circuit II will bedescribed. Components of the oscillation circuit I2 corresponding tothose of the oscillation circuit I I have been indicated by the samereference numerals with a prime figure added.

Oscillation circuit II comprises an electron coupled oscillator andincludes a pentode tube I3 which maybe of the commercially availabletype 6SJ7. Tube I3 includes an anode, a suppressor grid, a screen grid,a control grid, a cathode and a heater filament. The heater filament isconnected to and receives energy from the secondary Winding I4 of acombination stepup-stepdown transformer I5 having a line voltage primarywinding I6 and high voltage secondary windings II, I8, I9, and 20 inaddition to the secondary winding I4. The terminals of the primarywinding I6 are connected by conductors 2I and 22 to a commercial sourceof alterating current 23 through a fuse 24 and the switching mechanismshown in Fig. 4 and described hereinafter. Fuse 24 is provided toprotect the apparatus from damage due to excessive currents resultingfrom failure of a component of the apparatus. A lamp 24 connected acrossthe terminals of the transformer secondary winding I 4 is employed toprovide a visual indication that the switching mechanism of Fig. 4 isadjusted to its on position and that the apparatus is powered foroperation.

The control grid of tube I3 is connected through a parallel connectedresistance 25 and condenser 26 to one terminal of a parallel circuit 21,the other terminal of which is connected to ground G. The parallelcircuit 21 includes in one branch an inductance coil 28 and includescondenser 9 in another branch. The other branches of the parallelcircuit respectively include condensers 29, 30, and 3|. Condenser 3| isshown as adjustable in capacity and is provided for the purpose ofproviding a fine adjustment for the zero setting of the pencil I alongthe coordinate 2. Preferably the condenser 3I is provided with asuitable knob or kerf to facilitate its adjustment. Condenser 29preferably is of the type having a negative temperature coefiicient 0fcapacitance and is provided to compensate for the effect of ambienttemperature variations upon the frequency of the oscillating currentgenerated by oscillator I I.

The cathode of tube I3 is connected to ground G through an inductancecoil 32 which is disposed in inductive relation to the coil 28 andserves the purpose of feeding back energy from the putput QiIQuitof thetube I3 to thecircuit of the control grid for maintaining the circuit IIin an oscillating state.

Due to the coupling between the tuned circuit including coil 28 and thecircuit including coil 32, which latter circuit, excluding condenser32a, is also a tuned circuit because of distributed, wiring and tubecapacities, the impedance of the circuit including coil 32 is reflectedback into the circuit including coil 28. This effect tends to distortthe simple relationship between frequency and tuning capacity of asingle parallel resonant circuit and consequently, the movements of themark= ing element at the receiver tend to be non-linear with respect tothe movements of the transmitter stylus I. Such operation is undesirableand can not be tolerated .in a telautograph system in which accuracy ofreproduction of the transmitted material is of prime importance. Whilethis distortion can be kept small by loosel coupling coils 2B and 32, itcan be reduced still further to a negligible minimum by the use of acondenser 32a, connected in parallel with inductance coil 32. Condenser32a is so chosen as to tune the circuit including inductance coil 32 toa frequency which is approximately midway between the upper end of theoperating band of frequencies (over which the oscillating currentsproduced by oscillator I I are adapted to be varied as condenser 9 isrotated from one extreme position to the other) and the lower end of thecorresponding second harmonic band. 'It has been discovered that whencondenser 32a is so chosen the movements of the receiver marking elementare substantially linear with respect to the corresponding movements ofthe transmitter stylus I over the entire range of operation. Furtherexplanation of the operation of condenser 32a is thought unnecesaryinasmuch as the use of condenser 32a and its manner of selection asaforesaid comprise no part of the present invention but are disclosedand claimed in the application of Lloyd B. Cherry, Ser. No. 620,833,filed concurrentlv herewith, now Patent No. 2,480,? 13 of August 30,1949.

As shown. the screen grids of tubes I3 and I3 are connected throughrespective resistors 33 and 3'! to the positive terminal 34 of a filterindicated generally by the reference character 35 and having its inputterminals connected to the output terminals of a full wave rectifierdesignated by the character 33. The suppressor grids of tubes I3 and I3are connected directly to ground G.

The oscillating circuit of oscillator II includes the control gridcircuit of which the parallel circuit 21, including the variablecondenser 9, forms a part, and also includes the screen grid circuit,which may be traced from the positive terminal 3 through resistance 33,the screen grid of tube I3, the cathode thereof, and inductance coil 32to ground G, which, as shown, constitutes the negative output terminalof the filter 35. The screen grid and control grid circuits areinductively coupled by the inductance coils 2'8 and 32 and provide forhigh frequency operation through a range varying from approximately 390to 4'70 kilocycles, depending upon the position along the coordinate 2of the pencil I. Similarly, the inductance coils 28 and 32' ofoscillation circuit l2 provide for high frequency operation through afrequency range varying from approximately 3.90 to 470 kilocycles,depending upon the position of the transmitter pencil I along thecoordinate 3. Accordingly, the oscillation circuits II and i2 eachproduce a high frequency oscillating current having a frequency withinthe range of 390 to 470 kilocycles, depending upon the position to whichthe pencil I of the transmitter is moved relatively to the coordinates 2and 3.

Energizing current is supplied the anode circuits of the oscillationcircuits I I and I2 from the rectifier 36 and filter 35 through acircuit which may be traced from the output terminal 34 of filter 35through a conductor 42 to the junction of a pair of resistors 43 and 44.The other terminal of resistor 43 is connected to the anode of tube I3of oscillation circuit II, while the other terminal of resistor 44 isconnected to the anode of tube I3 of oscillation circuit I2. Thecathodes of tubes I3 and I3 are connected through their respectivelyassociated feedback coils 32 and 32' to ground G and thereby to thenegative output of filter 35. It is noted that ground G is connected bya resistor 45 to the junction of the transformer secondary windings I8and I9 whereby the potential of the junction point of windings I8 and I9is maintained suitably negative with respect to ground potential.

In order that both of the high frequency oscillating signals generatedby the oscillation circuits II and I2 may be amplified by a commonamplifier and both amplified quantities may be conducted over the sametransmission lines to the remotely located receiving station, theoscillating currents produced by the oscillation circuits 'II and I2 arealternately interrupted at a suitable frequency, and in particular, atthe frequency of the voltage supplied by source 23. To this end thereare provided keying and amplifying tubes 38 and 39. Tubes 38 and 39 alsoserve as buifer tubes to increase the stability of the respectivelyassociated oscillation circuits II and I2 by reducing fluctuations inthe oscillation circuit loads.

The use of tubes 38 and 39 for alternately interrupting the operation ofthe oscillators I I and I 2 and for serving the buffer purpose notedcomprises no part of the present invention but is disclosed and claimedin application Ser. No. 620,- 829, filed concurrently herewith by RudolfF. Wild, and Fred J. Curran, now Patent No. 2,457,- 790 of December 28,1948. The connections of tubes 38 and 39 in the circuit and their mannerof operation Will now be described.

As shown, each tube 38 and 39 includes anode, suppressor grid, screengrid, control grid, cathode, and heater filament elements. Energizingcurrent is supplied each of the heater filament elements from the lowvoltage secondary winding Id.

The output circuit of the oscillation circuit II is coupled by means ofa condenser ii! to the screen grid of tube 38 for amplifying andtransmission purposes, while the output circuit of oscillation circuitI2 is coupled by means of a condenser M to the screen grid of tube 39for the same purposes.

Energizing current is'supplied the anode circuits of the tubes 33 and 39from the rectifier 36 and filter 35 through a circuit which may betraced from the positive output terminal 33 of the filter to thejunction of resistors 33 and 31. The other terminal of resistor 3? isconnected to the anode of tube 38, while the other terminal of resistor33 is connected to the anode of tube 39. The cathodesof tubes 38 and 33are connected together and to the junction of transformer secondarywindings I8 and I9. Since the potential of the last mentioned junctionpoint is negative with respect to ground by anamount determined by themagnitude of resistor 45 and the magnitude of current flowing throughit, the anode voltage impressed on the tubes 38 and 39 is ofcorrespondingly greater magnitude than that impressed on the anodecircuits of tubes I3 and I3. Resistor 45, accordingly, is so chosen asto provide the proper operating anode voltages for tubes 38 and 39.

The suppressor grids of tubes 38 and 39, as shown, are directlyconnected to the cathodes of said tubes.

Energizing voltage is supplied the screen grids of tubes 38 and 39 fromthe rectifier 36 and filter 35 through a circuit which may be tracedfrom the filter output terminal 34 to the junction point of resistors 45and 46. The other terminals of resistors 45' and 46 are connected torespective screen grids of tubes 38 and 39.

Separate alternating voltages 180 out of phase with each other areimpressed on the control grids of tubes 38 and 39 from the transformersecondary windings I9 and. I8, respectively. Specifically, the cathodesof tubes 38 and 39, as previously noted, are connected together and tothe junction point of windings I8 and I9. The other terminal of windingI9 is connected through a resistor 41 to the control grid of tube 38,while the other terminal of winding I9 is connected through a resistor99 to the control grid of tube 39. The alternating voltages thusimpressed on the control grids of tubes 39 and 39 are of the propermagnitude to render the tubes 38 and 39 non-conductive during alternatehalf cycles of the alternating voltage supplied from the alternatingcurrent source 23.

In order to periodically interrupt the oscillating signals generated bythe oscillation circuits II and I2 at the frequency of the alternatingvoltage supplied from source 23, the screen grid of tube I3 is connectedto the junction of resistor 33 and the anode of tube 39 and the screengrid of tube I2 is connected to the junction of resistor 37 and theanode of tube 38. When tubes 38 and 39 are rendered conductive, thepotential of their respectively associated anodes decreases with respectto ground potential. The reduced anode voltages are sufliciently lowwhen appied to the screen grids of tubes l3 and I3 to cause the lattertubes to be rendered non-conductive. Hence, tube i3 is arranged to berendered nonconductive during the half cycle that tube 39 is conductive.During that half cycle tube 39 is non-conductive, and in consequence,tube l3 will be conductive and an oscillating signal will be produced byoscillation circuit I2. In the next half cycle tube 38 will beconductive and the oscillating signal produced by the oscillationcircuit I2 will be interrupted. During this latter half cycle the tube39 will be non-conductive, and as a result the oscillation circuit I Iwill be operative to produce an oscilating signal. The fluctuatingvoltages so created and impressed on the screen grids of oscillatortubes I3 and I3 change rapidly from a value at which the oscillators arepermitted to oscillate to a Value at which oscillation is interrupted,and consequently, the interruption and initiation of the state ofoscillation of tubes I3 and I3 is clean and sharp.

Specifically, assume that the voltage applied to the control grid oftube 38 is traversing its positive half cycle while the voltage appliedto the control grid of tube 39 is traversing its negative half cycle.The amplitude of the voltage applied to the control grid of tube 39 issufiicient to quickly block or out 01f conduction through time 3.9.Therefore, this tube is effectively eliminated from the circuit and thescreen grid of oscillator tube I3 receives its full operating voltagefrom the output terminal 34 of the filter 35. It is important to notethat during operation of the oscillation circuit II, the operatingvoltages applied to the electrodes of tube l 3 are constant for allpractical purposes, and consequently, no frequency modulations occur dueto periodically varying values of operating voltages.

During the half cycle under consideration tube 38 is conducting and thesteady D. C. component of its anode current effects a sharp decrease inthe voltage of its anode, which voltage is also the voltage applied tothe screen grid of oscillator tube I3, to such a value that conductionthrough the oscillator tube I3 is suddenly cut off. It is noted that out01f of tube I3 is readily accomplished because the anode voltage of tube38 may become zero or even go slightly negative with respect to thepotential of the cathode of tube I3 and still provide an operatingvoltage for the anode of tube 38 of amount sufficient to maintainconduction through tube 38. This operation is made possible because ofthe negative voltage applied to the tube 38 cathode by virtue of thelatters connection to the junction of transformer secondary windings I8and I9, which, as previously indicated, is negative with respect toground potential.

In the half cycle under consideration the tube 38 is utilized as abuffer for the oscillation circuit II and aso serves to amplify theoscillations produced by that oscillation circuit. To this end, theanode of tube I3 is connected by condenser 49 to the screen grid of tube38. It is noted that the circuit constants are not critical as long asthe most positive voltage which the anode of tube 38 may assume duringthis interval, determined by the direct current and radio frequencyvoltage drop across the anode resistor 31, is sufficient to preventoscillation of the oscillation circuit I2.

For the next half cycle of the voltage supplied by source 23, thereverse of the above conditions exists. That is to say, tubes 38 and I3are cut off while tubes 39 and I3 are rendered conductive. Hence, duringthis half cycle the osci lation circuit I2 produces an oscillatingsignal and this oscillating signal is amplified by tube 39 which alsoserves a buffer purpose. To this end, the anode of tube I3 is connectedthrough condenser lI to the screen grid of tube 39.

From the foregoing description it is evident that the interruption ofthe oscillating signals produced by the oscillation circuits II and I2are timed so that the oscillation circuit II generates an oscillatingsignal only when the oscillation circuit I2 is cut off and vice versa.Moreover, the interruption of the oscillating signals from theoscillation circuits II and I2 occurs at the frequency of thealternating voltage supplied from the source 23. In other words, duringone half cycle of the alternating voltage supplied by source 23, theoscillation circuit II is operative to generate an oscillating signaland that oscillation signal is amplified by the tube 38. During the nextalternate half cycle the oscillation circuit I2 is operative to generatean oscillating signal and that signal is amplified by the tube 39.Therefore, the tubes 38 and 39 which generate a voltage for interruptingone of the oscillating signals are also used to amplify the output ofthe other oscillation circuit during the cut off period of the firstoscillation circuit. The second tube 38 or 39'which generates a voltagefor interrupting the other osaeeqnai cillation circuit performs asimilar amplifying function for the first oscillating circuit. Thisamplification stage comprising tubes 38 and 39,. as previously noted,also serves to increase the stability of the oscillation of oscillationcircuits II and I2 by reducing fluctuations in the oscillation circuitloads.

In order to further amplify the oscillating signals generated by theoscillation circuits ii and I2 sufliciently for transmission of thoseoscillating signals to the remotely located receiving station orstations, there is provided an additional amplifier indicated generallyby the reference character 54. This amplifier 54 also performs theadditional function of matching the impedance of the output circuit ofthe transmitter to the impedance of the receiver or receivers to obtainmaximum power transference.

As shown, the transmitter amplifier 54 in-.

cludes a tube 55 which may desirably be of the commercially availabletype GACTI and includes anode, suppressor grid, screen grid, controlgrid, and cathode and heater filament elements. Anode voltage, issupplied tube 55 from the rectifier 36 and filter through a circuitwhich the filter through a resistor 59 to the screen grid,

the cathode and the parallel connected resistor 51 and condenser 58 tothe negative and grounded output terminal of the, filter. The screengrid is also connected by a condenser 60 to ground. The suppressor gridis connected directly to the cathode of tube 55.

The output circuits of the keying and amplifying tubes 38 and 39 arecoupled in parallel to the input circuit of the tube 55 so that themixing of the two oscillating signals derived from the oscillators IIand I2 takes place in this circuit. Specifically, the anodes of bothtubes 38 and 39 are connected by respective condensers 6| and 62 to thecontrol grid of tube 55, which, in turn, is. connected by resistor 62 toground G, and the cathodes of tubes 38 and 39 are connected throughresistor to ground G and through the parallel connected resistor 5.1 andcondenser 58 to the cathode of tube 55. Tube 55, therefore, operates toamplify the oscillating signals in the output circuits of both tubes 38and 39. The amplified quantity derived from tube is resistance-capacitycoupled by means of a condenser 63 and a resistor 64 to the inputcircuit of a tube 65 which is provided for the purpose of matching theimpedance of the output circuit of transmitter amplifier 54 to thecharacteristic impedance of a transmission line connecting thetransmitter to the remotely located receiver.

Tube 65 may be of the commercially available type 6V6 and includes ananode, a screen grid, a control grid, a cathode, a heater filament, andalso beam forming plates. Energizing voltage is supplied the anodecircuit from the rectifier .36 and filter 35 through a circuit which maybe traced from the positive output terminal 34 to the anode .of tube 65,the cathede thereof, and through an Output resistor 66 to the negativevoltage is supplied the screen grid of tube through the same circuit.The beam forming plates, as shown, are directly connected to thecathode. The control grid of tube 65, as shown, is directly connected tothe junction of condenser 63 and resistor 64 and thereby is coupled tothe output circuit of tube 55.

While the rectifier 36, filter 35, and transmit: ter amplifier 54 havebeen shown in Fig. 1 as being located closely adjacent the plottingboard 4, it will be understood that, if desired, these components may belocated at a distance with respect to the plotting board and also Withrespect to the oscillation circuits H and I2. For example, in someapplications it may be desired to locate the plotting board 4 and theoscillation circuits ll and [2 in one room and to have the rectifier 36,filter 35, the transmitter amplifier 54, and the switching mechanism, towhich reference has previously been made, in another room to the endthat the transmitting mechanism visible for manipulation by an operatormay be made less cumbersome and bulky. This feature is also advantageouswhen the transmission system of the present invention is utilized onshipboard in which the space avail-. able is at a premium and wouldpreclude the location of all of the transmitting equipment closelyadjacent the plotting board 4 and overhead transmitter unit 5. In apractical operating embodiment of the present invention, a shieldedcable 25 feet long is provided between the plotting board and thecircuit components including the rectifier 36, filter 35, amplifier 54,and the switching mechanism.

Tube 65 is connected to operate as a cathode follower. That is to say,the output signal which is transmitted to the receiver is derived fromthe resistor 66 connected in the cathode circuit of the tube. Resistor66 is so chosen as to have a characteristic impedance approximating thatof the transmission line L connecting the transmitter to the receiver.As shown, the terminal of resistor 56 which is connected to the cathodeof tube 65 is coupled by a condenser 67 to one conductor L of thetransmission line L through the switching mechanism, While the other andgrounded terminal of the resistor 66 is connected through said switchingmechanism to another terminal L of the transmission line.

At. the transmitter amplifier 54 there is also provided a relay 68, oneterminal of which is connected to the ungroundcd side of filamentsecondary winding iii and the other terminal of which is arranged to beconnected .to the grounded side of winding- !4 upon closure of theswitch 1 attached to the writing pencil or stylus I. ,To this end, oneterminal of the switch I, as shown, is connected directly to ground G.When the switch i is closed, as upon movement of the stylus i intoengagement with the plotting board 4, the relay 68 is energized andcloses an associated switch 65 to energize a solenoid "i6, shown in Fig.2, which is attached to the marking element or recording pen mechanismfor moving the latter into engagement with the recording chart. When theswitch i is open and the relay 68 is deenergized, the switch v6.6 isalso open, and the pen at the receiving unit is moved out of engagementwith the recording chart by the action of gravity, the solenoid it thenbeing deenergized.

As has been previously mentioned, the transmitter mechanism shown inFig. 1 is adapted to be utilized in conjunction with a plurality ofinvand grounded terminal of the f1 lter,. Energizing dependentlyoperable receivers. In order to permit one or more of the receivers tobe placed in or removed from operation the switching mechanism shown inFig. 4 is provided for selectively connecting the output circuit of thetransmitter amplifier 3 to one or more of the receivers. The switchingmechanism of Fig, 4 includes three separate banks, designated A, B andC, respectively, of switches and is adapted to selectively connect theoutput circuit of transmitter amplifier 54?. to as many as threereceivers. If it is desired to operate additional receivers from thetransmitter, it is necessary only to supply such additional receiversand a switch bank associated with each receiver. As the number ofreceivers is increased, however, the current carrying capacity of tube65 must be correspondingly increased.

In the arrangement specifically illustrated, the output circuit oftransmitter amplifier 54 is adapted to be connected by means of thethree switches A, B, and C of Fig. 4 and a transmission line Lassociated with each of the switches to any number of three receivers. Adummy load" resistor is associated with each of the switches A, B, and Cfor connection to the output circuit of the transmitter amplifier 5 whena receiver is removed from operation for the purpose of maintainingconstant the load into which the transmitter amplifier 54 worksregardless of the numberv of receivers in use, said resistors being ofthe proper magnitude to accomplish this result. A more detaileddescription of the switching mechanism of Fig. 4 and the manner in whichsuch load compensation is effected is given hereinafter. For purposes ofillustration it is assumed that the switch A of Fig. i is arranged toconnect the transmitter of Fig. 1 to the receiver of Fig. 2.

.As has been previously mentioned, each of the remotely locatedreceivers for reproducing the transmitted material is arranged totranslate the adjustable frequencies of the oscillating signalsgenerated by the oscillation circuits H and [2 into two coordinates ofpen position. More specifically, the receivingapparatus operates to movethe recording pen in a vertical direction in accordance with thevariations in frequency of the oscillation signal generated by theoscillation circuit 5 I, and operates to move the recording pen in ahorizontal direction in accordance with the frequency variations of theoscillation signal generated by the oscillation circuit i2. In thismanner the changes in position of the pencil or stylus along theplotting board 4 at the transmitter may be exactly reproduced at thereceiving apparatus.

By reference to Fig. 2, it will be noted that two independent receivingcircuits are provided at each receiver. One of the receiving circuitscontrols the movement of the recording pen in one coordinate, forexample, the horizontal coordinate, and the other receiving circuitcontrols the recording pen in the vertical coordinate. The oscillatingsignals derived from each of the oscillation circuits ii and i2 andtransmitted to the receiver over the transmission line L are impressedon both of the input circuits of the -two receiving circuits. Thereceiver mechanism is so arranged that one of the receiving circuits isresponsive only to the oscillating signal generated by the oscillationcircuit H, and the second receiving circuit is responsive only to theoscillatsignal generated by the other oscillation circuit i 2 to controlthe energization of individually indicated at 83.

linked by suitable mechanical means to the re cording pen to positionthe latter in the two coordinates along the recording chart. Theoperation of the two receivingcircuits is the same and the followingexplanation applies to both circuits. One of the receiving circuits hasbeen generally indicated by the reference character TI and the other bythe reference character H. The elements of the receiving circuit llcorresponding to those of the receiving circuit II have been indicatedby the same reference numerals with a prime figure added.

The receiver ll includes two stages of amplification, the first of whichutilizes an amplifying tube 12 of the commercially available type 6A0?and the second of which utilizes an amplifying tube 13 of the type 6V6.In the second stage of amplification the two oscillating signals fromthe transmitter are separated and one of them is rejected. In otherwords the second stage of amplification responds only to the oscillatingsignal generated by one of the oscillation circuits l I or 82 and, forpurposes of illustration, will be assumed to respond only to theoscillating Signal generated by the oscillation circuit ll. Rejection ofthe oscillating signal from the oscillation circuit 12 is accomplishedin a manner described in detail hereinafter, and generally speaking,involves the application of an alternating voltage derived from source23 to periodically interrupt the conduction of tube 13. The oscillatingsignal after rejection of the undesired portion con sists of a radiofrequency Wave which is periodically interrupted at the frequency of thevoltage supplied by the source 23 and has been illustrated schematicallyin graphs 1) and bb of Fig. 3 which show the oscillating signalfrequency as being higher and lower, respectively, than a frequencyvalue at which the receiving pen is held motionless along the verticalcoordinate.

Tube 12, as shown, includes anode, suppressor grid, screen grid, controlgrid, cathode, and heater filament elements. Energizing current issupplied the heater filament from the low voltage secondary winding 1'4of a transformer 15 having a line voltage primary winding 16 which isconnected by conductors 1'8 and 19 to the alternating voltage source 23.To this end the conductors l8 and 19 are included in the shielded cableL connecting the transmitter to the receiver. The transformer 15 alsoincludes high voltage secondary windings and 8|, both of which areprovided with a center tap.

Energizing voltage is supplied to the anode of tube 12 from a full waverectifier indicated generally by the reference numeral 82 and a filterThe rectifier 82, energized by the transformer secondary winding 80,provides a voltage at the output terminal 8 1 of the filter 83 which issuitably positive with respect to the potential of ground G to which thenegative terminal of the filter is connected. As shown, the positiveterminal 84 is connected through a resistor 85 to the anode of tube 12,and the cathode is connected through a parallel connected resistor 86and condenser 81 to ground G. Energizing voltage is supplied to thescreen grid of tube 12 from the positive filter output terminal 84through a circuit, including a resistor 88, to the screen grid and fromthe cathode through the parallel connected elements 88 and 81 to groundG. The screen grid is also connected to ground G by a condenser 88a, asshown.

As may be seen by reference to Figs. 1, 2 and 4, the output terminal ofresistor 66 of the transmitter amplifier 54, which is connected to thecathode of tube 65, is connected by condenser 61, switch A of theswitching mechanism of Fig. 4, and conductor L of the shieldedtransmission line L to the control grid of tube l2. The other andgrounded output terminal of the transmitter amplifier 54 is connectedthrough conductor L of the transmission line L to the parallel connectedelements 853 and ill and thereby to the cathode of tube '52. The gridand cathode of tube it are connected by a resistor 3601. having a valueapproximating the characteristic impedance of the transmission lines Land L thus terminating the transmission line in its characteristicimpedance. Resistor 86a serves to connect the grid and cathode of tube72 also but if desired a separate resistor may be utilized for each tubein which case each resistor will have a value twice the value ofresistor 86a.

The output circuit of tube 72 is coupled by a condenser as and aresistor 90 to the input circuit of tube it. Tube it includes an anode,a screen grid, a control grid, a cathode, a heater filament, and beamforming plates. Energizing current is supplied to the heater filamentfrom the low voltage transformer secondary winding M.

Anode voltage is supplied to tube '53 through a circuit path which maybe traced from the positive output terminal 8:1 of the filter 83 througha parallel network including in one branch the primary winding 95 of atransformer 96 to the anode of tube 13, the cathode thereof, and aparallel connected resistor 92 and condenser 93 to the grounded andnegative terminal of the filter. The other branches of the parallelnetwork respectively include a resistor 9| and a condenser 9d. Thetransformer 95 comprises a part of a frequency discriminator indicatedgenerally by the reference numeral 9'! and includes a split secondarywinding in addition to the primary winding 95.

The beam forming plates of tube 73 are directly connected to thecathode, and the control grid is coupled to the output circuit of tubel2 by virtue of its connection to the junction of condenser 89 andresistor 90.

Alternating voltage is impressed on the screen grid of tube 13, forperiodically rendering it non-conductive, from one half of the centertapped transformer secondary winding 89 through a circuit which may betraced from the lower terminal of the winding 80, as seen in thedrawing, through a resistor 98 to the screen grid of tube E3 and throughthe parallel connected elements 92 and 93 to ground and thereby to thecenter tap on winding 80. The screen grid of tube 13 is also connecteddirectly to ground G by a condenser 99. The magnitude of the alternatingvoltage impressed on the screen grid of tube 13 is so chosen as to besufilcient to cause the tube 13 to be rendered non-conductive or cut offduring those half cycles of the voltage of source 23 in which the screengrid is driven in the negative direction. Furthermora'the phase of thisalternating voltage is such that the tube 13 is operative to amplify theoscillating signals generated by the oscillation circuit I I andtransmitted to the receiver H only during those alternate half cycles ofthe supply line voltage in which the oscillation circuit ll is operativeto generate an oscillating signal.

It is noted that the entire transmission system receives energizingcurrent from the single source 23 of alternating current. This source,as. described, is impressed on the telautograph system through theswitching mechanism of Fig. 4, which. switching mechanism is locatednear the transmitter amplifier unit, and the alternating currentutilized for energizing the various receivers is transmitted from thesource 23 by way of the individually associated transmitting cable L.This is done toinsure synchronism of the keying action of thetransmitter and receiver units. and also provides the advantage ofpermitting the installation and use of receivers at locations wherethere is not available alternating power of the same frequency and phaseas that delivered by source 23.

The frequency discriminator 97, previously referred to, includes inaddition to the transformer 96 a pair of diode rectifiers I00 and NI,which desirably may be contained within a sigle en velope, generallydesignated at Hi2. One half of the split secondary winding of theintermediate frequency transformer 9E5 has been designated by thenumeral m3 and the other half by the nu.- meral Hi l. The center tap ofthe split secondary winding comprising the junction of winding sectionsI03 and Hit is connected through a blocking condenser [55 to the anodecircuit of tube 73, and more specifically, to the negative terminal ofthe primary winding 95. The center tap of the split secondary winding isalso connected to the point of engagement of a pair of resistors H36 andNH. The resistors I06 and llll' are shunted by a resistor I08 which isprovided with an adjustable tap 169. The usable output voltage from thefrequency discriminator is obtained across the resistor H18 which, asshown, is shunted by a condenser H0.

The diode rectifiers Hi0 and Hill may be contained within a single tubesuch as the commercially available type 6H6. Each diode includes anode,cathode, and heater filament elements. The heater filament elements areconnected in series with each other and receive energizing current fromthe transformer secondary winding 14. The cathodes of the diodes I00 andI0! are connected through resistors H16 and I01, respectively, to thejunction of the transformer secondary windings 193 and IE4. The otherterminal of the winding I03 is connected to the anode of diode I-llll,while the other terminal of the winding IE4 is connected to the anode ofthe diode 10!.

For tuning the secondary winding of the transformer 96 to the frequencyof the oscillating signals impressed thereon from the output circuit oftube 13, a variable condenser III is provided. This variable condenseris arranged to be automatically adjusted in capacity as required tomaintain the secondary winding of the intermediate frequency transformer96 tuned to the frequency of the applied oscillating signals. A variablecondenser l i2 and a variable inductance i It are connected in shuntwith the secondary wind ing of the transformer 96 for a purpose whichwill be later explained.

The blocking condenser I05 and the condenser I I8 are so selected as topresent low impedance to the radio frequency oscillating currentsflowing through them. The condenser 94 and the transformer primarywinding 95 connected in parallel therewith are so selected as to providehigh impedance in order to produce a large output signal from thediscriminator. Preferably the primary winding 95 is tuned to a valuewhich is outside the range of frequency variation of the oscillatingsignals generated by the oscillation circuit l l at the transmitter andimpressed on the receiver circuits... By .way of example it is notedthat satisfactory operation has been obtained when the primary winding95 is tuned to a frequency of 325 kilocycles. The tuning of the primarywinding 95 to this value which is below the operating range of frequencyvariation of the oscillating signals conveyed by the transmission line Lto the receiver II is being disclosed and claimed in my application,Ser. No. 620,831, filed concurrently herewith, now Patent No. 2,473,401of June 14, 1949.

The frequency discriminator 91 together with the diodes I and IN isprovided for the purpose of deriving a voltage having an alternatingcomponent of one phase or of opposite phase and of the same frequency asthe voltage supplied by source 23 accordingly as the frequency of theoscillating signal impressed thereon from the output circuit of tube I3is higher or lower than the frequency value to which the split secondarywinding of transformer 96 is tuned. The details of this frequencydiscriminator constitute no part of the present invention. Its manner ofoperation and arrangement is disclosed in my prior application, Ser. No.537,505, filed May 26, 1944, and therefore, need be only brieflydescribed herein.

It is believed suificient to note that if the frequency of the appliedoscillating signal is the value to which the secondary wind ng of theintermediate frequency transformer 96 is tuned, the outputs of the dioderectifiers I00 and IOI cancel each other and zero voltage appears acrossthe output resistor I08 of the frequency discriminator circuit 97. theapplied oscillating signal is a value other than that to which thesecondary winding of the transformer 96 is tuned, the phase relations ofthe voltages applied to the diode rectifiers I00 and I0! are such thattheir outputs do not cancel and a direct current voltage appears acrossthe output resistor I08. The polarity of this voltage depends uponwhether the frequency of the applied oscillating signal is above orbelow the value to which the secondary winding of the discriminator istuned. The magnitude of the voltage depends upon the extent of departureof the frequency of the applied oscillating signal from the value towhich the secondary winding is tuned.

Recalling now that the oscillating signal which is applied to thefrequency discriminator 91 is an intermittent radio frequency wave asshown in graphs b and DI) of Fig. 3, it will be seen that the voltageappearing across the output resistor I08 of the discriminator will be anintermittent or pulsating direct current voltage whose polarity andmagnitude are as stated above. Furthermore since the applied oscillatingsignal is periodically interrupted at the frequency of the alternatingvoltage supplied by source 23, the pulsations of direct current voltageproduced across resistor I08 have the same frequency as the voltagesupplied by source 23. Graphs c and cc of Fig. 3 illustrate the voltageoutput produced across the resistor I08 for the respective cases of highand low frequency of the applied oscillating signal.

The pulsating voltage produced across the resistor I08 may be consideredas comprising two components, (1) a steady D. C. component and (2) an A.0. component. The A. C. component obtained when the frequency of theapplied oscillating signal is higher than the value to which thesecondary winding of the frequency dis- 1 j 'criminator is tuned isshown in graph 11 of Fig. 3 whilergraph dd of Fig. 3 illustrates the/A.C.

If the frequency of component obtained when the frequency of the appliedoscillating signal is lower than the value to which the secondarywinding of the frequency discriminator is tuned.

The variable condenser H2 connected in parallel with the discriminatorsecondary winding is a trimmer condenser and serves to provide for zeroadjustments of the recording pen along the vertical coordinate. To thisend the condenser H2 is provided with a suitable knob or kerf forfacilitating its adjustment.

In order to provide for span adjustment or, in other words, the extentof variation of condenser III required to traverse the entire frequencyrange of operation, the variable inductance H3 is provided. InductanceH3 is preferably provided with an adjustable iron core. A suitable knobor kerf is preferably provided on the inductance H3 to facilitate itsadjustment.

The alternating component of the pulsating voltage produced acrossresistance I08 is amplified by a stage of voltage amplificationincluding a tube H4, which stage of amplification incorporates a gaincontrol for manually adjusting the sensitivity of the receiving unit.This gain control comprises the provision of slider contact I09 inassociation with the resistor I08 for tapping 01f and impressing on theinput circuit of tube I I4 a variable portion of the voltage producedacross the resistor I08. Tube H4 may be of the commerciall availabletype 6AC7 and includes anode, suppressor grid, screen grid, controlgrid, cathode, and heater filament elements. Energizing current issupplied the heater filament from the transformer secondary winding I4.Anode voltage is supplied tube H4 from the rectifier 82 and the filter83 and to this end the positive terminal 84 of the filter 83 isconnected through a resistor H5 to the anode of tube H4 and the cathodeof the latter is connected through a resistor I I6 to the grounded andnegative terminal of the filter. Energizing voltage is supplied thescreen grid through a circuit which ma be traced from the positiveterminal 84 through a resistor III to the screen grid, the

' cathode and resistor H6 to the grounded and negative terminal of thefilter. A condenser H8 is connected between the screen grid of tube H4and ground, as shown.

The output circuit of tube H4 is coupled by a condenser H9 and aresistor I20 to the input circuit of a motor drive stage indicatedgenerally by the reference character I2I. Motor drive stage I2I is shownas including triodes designated by the numerals I22 and I23,respectively, but it is preferred to utilize a number of such triodesconnected in parallel with each other instead of single triodes. Forexample, in a practical operating embodiment of the invention, threesuch triodes I22 and I23 are connected in parallel, thus insuring thederivation from the motor controlled by the tubes of sufficient torqueto actuate the recording pen.

As shown, the tubes I22 and I23 each include anode, control grid,cathode, and heater filament elements. Energizing voltage is suppliedthe heater filament elements in series from the transformer secondarywinding I4. Anode voltage is supplied tubes I22 and I23 from thetransformer secondary winding SI and to this end one end terminal ofwinding 8| is connected to the anode of tube I22 and the other endterminal of that winding is connected to the anode of tube I23. Thecathodes of tubes I22 and I23 are connected together and through abiasing resistor I24 to one terminal of the control winding I25 of areversible two-phase induction motor I26. In addition to the Winding.I25; the motor. I26 includes a second winding I2I. A condenser I28'isconnected in parallel with Wind'- ing I25 and the other terminal of thelatter is connected to the center tap of the transformer secondarywinding 8|. Accordingly, energizing current is delivered to the motorWinding I25 from the transformer secondary winding 6f under control ofthe triodes I22 and I23. Winding I21 of the motor I26 is connectedthrough a condenser I29 and conductors I8 and T9 to the source ofalternating current 23.

Thus, the output current of the tubes I22 and I23 is utilized to deliverenergy to winding I25 of the motor I26 and the secondary winding I21 ofthat motor is connected to the alternating current power supply throughcondenser I23. The motor is actuated for rotation when an alternatingcurrent signal of the frequency of the voltage supplied by source 23 isimpressed on the input circuits of. tubes I22 and I23. For accomplishingthis result the control grids of. triodes I22 and I23 are. connectedtogether and to the junction of condenser H3 and resistor I23.

Referring to graphs (1 and dd of Fig. 3, it will be seen that the A. C.component of the discriminator output voltage reverses in phase when thefrequency of the applied oscillating signal changes from below to abovethat to which; the frequency discriminator. is tuned. This change inphase when applied to. the control grids of triodes I22 and I23 causes adecrease in the conductivity of one triode I22 or I23 and acorresponding increase in conductivity of the other triode. Inconsequence, energizing current is delivered to. the control winding I25of the motor I26 which is of one phase or of opposite phase relative tothe voltage of source 23 depending upon which triode I22 or I23 has hadits conduction increased. Stated differently, this change in phase ofthe voltage derivedfrom the frequency discriminator causes reversal ofthe direction of rotation of the reversible motor I26.

The details of this motor drive circuit comprise no part of the presentinvention since this circuit is the invention of Walter P. Wills and isdisclosed in a copending application, Ser. No. 421,176, filed December1, 1941, now Patent No. 2,423,540 of July 8, 1947, and hence, requiresno further description herein.

The shaft of motor I26 is geared in any suitable manner, not shown inorder to avoid complication of the drawing, to the. variable condenserIII connected in the frequency discriminator. The shaft of motor I26 isalso mechanically coupled to the recording pen of the receiver andadjusts both the condenser III and the recording pen until the secondarywinding of the frequency discriminator is tuned to the frequency of theapplied oscillating signal. Inasmuch as the Output of. the frequencydiscriminator is zero when it is tuned to the frequency of the appliedoscillating signal, the motor then stops and is maintained stationaruntil the frequency of the applied oscillating signal again changes.

In Fig. 2 a portion of the receiving instrument containing the recordingchart is broken away to show a pen carriage I30 located beneath thechart I38 and having a pen I3I mounted thereon. The pen' I3I is arrangedto be lifted by the solenoid I0 up into engagement withthe chart I38, asuitable writing platen of glass or other suitable transparent materialbeing arranged closely adjacent the top of. the chart to. providebacking for the chart.

"The carriage I36 is actuated for movement in vertical and horizontaldirections by bars I32.and I33, respectively. The supporting bars forthe carriage have rollers I34 and I35, respectively, on their ends,which ride on individually associated tracks I36 and I31, which areprovided in the base of the receiving instrument. As the rods I32 andI33 are moved, the pen carriage I30 will be moved in any directionunderneath the chart I38. If rod I32 only is moved, as upon operation ofmotor I26, the carriage I33 will be moved in a vertical direction only.Similarly, if rod I33 only is moved, as upon operation of motor I26, thecarriage I36 will be moved in a horizontal direction any. If rods I32and I33 are simultaneously moved, the pen carriage I30 will be moved atan angle to both sides of the instrument. Movement is imparted to therod I32 as previously stated by the motor I26, which has a drive pulleyI39 attached to it. This pulley drives a cable I46 that passes oversuitable guide pulleys at opposite ends of the track I36 and which isfastened to the roller I34. In a like manner motor I26 is utilized toimpart movement to the rod I33, and to this end motor I26 has a drivepulley i llfastened to its shaft. As the pulley MI is rotated, it drivesa cable I42 that passes around suitable guide pulleys at the ends oftrack I31 and which is attached to the roller I35.

' In consequence, as the motors I26 and I26 are 'energ'ized'for rotationin one direction or the other in response to the reception "ofoscillating signals from the transmitter, the pen I3I will be adjustedrelatively to the chart I38 to produce an exact reproduction of themovement imparted, to the writing stylus or pencil at the transmitterrelatively to the plotting board 4. As previously'noted, upon movementof the writing stylus or pencil into engagement with the plotting boardat the transmitter, the switch "I is closed and effects energization ofthe solenoid I3, for lifting the recording pen up into engagement withthe under side of the recording chart I38. In consequence the recordingpen I3I is operative to trace the path of its movement on the chart I38only when the writing pencil or stylus at the transmitter is in contactwith the plotting board.

This arrangement in which the recording mechanism is located entirelybeneath the chart, and therefore, leaves the top of the chart free forinspection and other purposes constitutes no part of the presentinvention but is the invention of Barnes, Johnson and Wills and isdisclosed and claimed in application Ser. No. 620,828, filed by themconcurrentl herewith.

As noted previously the transmitter of Fig. 1 is arranged to be utilizedin conjunction with a plurality of receivers as shown inFig. 2 and whichare operable independently of each other. To this enda separatetransmission line or cable is provided between each of the receivers andthe transmitter. The reference character L designates the transmissionline provided between the transmitter of Fig. 1 and the receiver shownin Fig. 2. In order to permit one or more of the plurality of receiversto be placed in or removed from operation, the switching mechanism shownin Fig. 4 is provided. The switch bank A is provided for connecting thetransmitter of Fig. l to the receiver shown in Fig. 2. All of thevarious 19 switch banks provided for connecting the transmitter to theindividual receivers may be alike and, therefore, only the switch bank Awill be described.

Referring to Fig. 4 it will be noted that the switch bank A comprises a5-gang switch including gangs which have been respectively indicated bythe reference numerals I43, I44, I45, I46, and I41. Each gang isprovided with eight relatively stationary contact segments a through hequally spaced from each other on a circle and which are insulated fromeach other, and also with a movable contact arm 7' which is pivoted forrotation at a center point and is provided with an arcuate contactsegment k at one end and with an arcuate contact segment m at its otherend. The contact segments is and m are also insulated from each other.The switch arms 1' for all of the gangs are mounted for rotation on thesame shaft and are arranged to be rotated as by manipulation of a knobI48 which has been provided for that purpose. The contact segments k andm are of the proper lengths to connect two adjacentcontact segments a-hat diametrically opposite portions on the circle on which the contactsegments ah are arranged.

The 5-gang switch is utilized as a three-position switch to provide anoff position, a standby position, and an on position. The 5-gang switchis shown in its off position in Fig. 4. In this position it will benoted that the arcuate contact segment is in each gang is arranged toconnect the contact segments a and 19 while the arouate contact segmentm is arranged to connect the contact segments e and f. In its stand-byposition the arcuate contact segment k of each gang is arranged toconnect the contact segments 1) and while the arcuate contact segment mis arranged to connect the contact segments f and g. In its on positionthe arouate contact segment It in each'gang is arranged to connect thecontacts 0 and d, while the arcuate contact segment m is arranged toconnect the contact segments 9 and h.

With this switching arrangement wired as shown in Fig. 4, thealternating current supply source 23 is disconnected from both thetransmitter and the receiver when the switch is in its ofi position.While in this position the conductor over which the high frequencyoscillating currents from the transmitter are conveyed to the receiveris broken as is also the ground connection. In addition the circuit forenergizing the pen lifting solenoid I8 is open. A dummy load resistor m9is then connected to the output terminals designated by the referencenumerals I56 and II of the transmitter amplifier 54. The circuit throughwhich the dummy load resistor I 49 is connected to the transmitteroutput terminals I50 and I5I may be traced from the output terminal I50to a conductor I52 to the contact segment f of gang I47, through thearcuate contact segment m to the contact segment e through resistor I49and a conductor I53 to the transmitter amplifier output terminal i 5I Inits stand-by position the S-gang switch is operative to supply power toboth the transmitter and receiver from the alternating current source 23and the dummy load resistor I49 is maintained connected to thetransmitter output terminals I5fi and I5I. In this position of theswitch the high frequency, ground and pen lifting connections from thetransmitter to the receiver are broken.

V 'Thecircuit through which alternating current is supplied to thetransmitter may be traced from one terminal of the alternating currentsource 23 through a conductor I54 to the contact segment 9 of the switchgang I43 through the arcuate contact segment m to the contact segment Iand through a conductor I55 to the output terminal I56 of thetransmitter. By referring to Fig. 1 it will be noted that this outputterminal I56 is internally connected in the transmitter through fuse 24and the primary winding I6 of the transformer I5 to the transmitteroutput terminal I51, As seen in Fig. 4 the output terminal I51 of thetransmitter is connected by conductor I58 to the contact segment 1 ofswitch gang I44, which contact segment is connected through arouatecontact segment m to contact segment g. The contact segment g isconnected by a conductor I59 to the other terminal of the alternatingcurrent source 23.

The circuit through which alternating current energy is supplied to thereceiver from the alternating current source 23 may be traced from oneterminal of the source 23 through conductor I54 to contact segment 0 onswitch gang I43 through arouate contact segment k to contact segment bthrough a conductor I68 and through a conductor L v provided in thetransmission line or cable to the energizing conductor I9 provided inthe receiver. The other energizing conductor I8 of the receiver isconnected through a transmission line conductor L to a conductor I6I inthe switch mecham'sm which is connected to contact segment b on theswitch gang I44. That contact segment is connected by arouate contactsegment k to contact segment 0 and by conductor I59 to the otherterminal of the alternating current source 23.

The circuit which connects the dummy load" resistor M9 to thetransmitter amplifier output terminals I50 and I5I may be traced fromthe said output terminal I56 through conductor I52, contact segment 1 onswitch gang I47 through arouate contact segment m to contact segment gthrough resistor I49 and conductor I53 to the transmitter amplifieroutput terminal I 5I.

When the switch is in its on position, power is supplied to both thetransmitter and receiver, the high frequency, ground and pen liftingcircuits are completed, and the dummy load resistor I49 is disconnectedfrom the circuit.

The circuit through which power is supplied to the transmitter from thealternating current source 23 may be traced from one terminal of thesaid source through conductor I54 to contact segment or of switch gangI43 through arouate contact segment m to contact segment h and throughconductor I55 to the energizing terminal I56 of the transmitter. Theother energizing terminal I51 of the transmitter is connected throughconductor I58 to the contact segment h of switch gang I44 througharouate contact segment m to conductor I59 and thereby to the otherterminal of the alternating current source.

The circuit through which energizing current is supplied the receivermay be traced from one side of the source 23 to the conductor I54 tocontact segment 0 on switch gang I43 through arouate contact segment k:to contact segment d and conductor I65 and transmission line conductor Lto the receiver energizing conductor 19. Energizing conductor I8 of thereceiver is connected through transmission line conductor L andconductor IBI to contact segment at on switch gang I44 through arouatecontact segment 70 to contact segment 0 and conductor I59 to the otherterminal of source 23.

of: the solenoid I in the receiver.

- In this position of the switch theoutputter= m-i-nal- I50 of thetransmitter amplifier 54 is connected to the receiver through a circuitwhich may be traced from said output terminal I59 through conductor I52to contact segment 0 on switch gang I41 through arcuate contactsegment kto contact segment (1 through a conductor I62 and through transmissionline conductor L to the control grids of tubes "I2 and 12' in thereceiver. The grounded output terminal II of the transmitter amplifier54 is connected through the conductor I53 to contact segment h onswitchgang I45 through arcuate contact segment m to con-tact segment 9to contact segment 0 through arcuate contact segment It to contactsegment at through a conductor I64 and transmission line L to thegrounded conductor in the receiver.

The circuit for energizing the pen lifting solenoid ID in the'receivermay be traced from one terminal of alternating current source 23 throughconductor I54 to contact segment g on switch gang I43 through arcuatecontact segment m to contact segment it through conductor I55 to thetransmitter output terminal I55, through fuse 24, switch 69 totransmitter output terminal I65, conductor I66 to contact segment 0 onswitch gang I46 through arcuate contact segment 70 to contact segment a.through a conductor I61 and transmission line conductor L to oneterminal The other terminal of the solenoid IE3 is connected throughconductor I8, transmission line conductor L conductor IGI to contactsegment 11 on switch gang I44 through arcuate contact segment is tocontact segment 0 and through conductor I59 to the other terminal ofsource 23.

From the foregoin explanation itmaybe readily seen that any one of aplurality of receivers may be connected to or disconnected from theoutput terminals of the transmitter, as desired. In order to maintainthe signal level at the input circuits of the receiver or receiversconstant in operation regardless of the number of receivers in use atany time, the dummy load resis'tors I49 are provided. The dummy loadresistors I49 are so chosen as to have an impedance approximating thatof the characteristic impedance of each associated transmission line orcable. For example in a satisfactorily operating embodiment of thepresent invention the characteristic impedance of each transmission lineL was found to be 65 ohms. In the said embodiment, therefore, the dummyload resistors I49 were each assigned a value of 65 ohms.Consequentlmthe transmitter power amplifier 54 experiences no change inload when a receiver is removed from the telautograph system and thesignal level input to the receiver or receivers in operation remainsconstant regardless of the number of receivers in operation.

It is noted that the impedance into which the transmiter power amplifier5d works is a function of the number of receivers which are operatedfrom that transmitter. For example, when the characteristic impedance ofeach transmission line is 65 ohms and six receivers are arranged foroperation from the transmitter, the effective impedance load into whichthe transmitter power amplifier 54 works is approximately 11 ohms. Anyattempt to match the internal impedance of power amplifier 54 to theimpedance of this effective load would require the parallel operation ofa relatively large number of high gain tubes. In order to permit the useof a single output tube 65, the output circuit of that tube is connectedas a cathode follower to produce a '22: reasonablesignal ever at theinput: circuit of eachtransmission line-and any loss of signal due.tomismatching is, compensatedfor by; providinggreater amplification atthe receivers. The tubes I2- and I2 ateach receiver provide such greateramplification as may be necessary. 7

While in accordance with th provisions of the statutes, Ihaveillustrated and describedthe best forms of the invention now known to,me, it will. be apparent to those skilled in the art that, changes maybe made in the form of theapparatusdisclosed without departing from thespirit of the invention as set forth in the appended: claims, and thatin some cases certain features of the invention may sometimes be used toadvantage without a correspondin use of other features.

Having now described my invention, what I claim as new and desire tosecurev by Letters. Patent, is;

1. Apparatus for selectively transmitting intelligencetoone or more of aplurality of receiving stations from a transmitting stationincludingmeans at said transmitting station to: produce electricalcurrents representative of the intelligence to be transmitted,reproducing mechanism at each of said receiving stations and responsiveto a. characteristic of said electrical currents to reproduce thetransmitted intelli gence, a common source of electrical current tosupply energizing current to said transmitting. and receivingstatic-11s,. an individualv cable connecting each of said receivingstations to: said transmitting station, each of said cables providing. atransmission circuit for said source of.

energizing current to the associated receiving;

station and providing a transmissioncircuit path for saidelectrical'currentsfrom said transmitting station to the associatedreceiving station, and switching means associated with each or". said.cablesand operative in one condition of adjustmerit to disconnect saidsource of electrical enei gizing current from both the transmitting.and. receiving stations and operative in. another conditi'on ofadjustment to. connect said source of. electrical. energizing current tosaid transmitting and receiving stations.

2. Apparatus for selectively transmitting intelligence to one or more ofa plurality of receiving stations from a transmitting station includingmeans at said transmitting station to produce electrical currentsrepresentative of the intelligence to be transmitted, reproducingmechanism at each of said receiving stations and responsive to acharacteristic of said electrical current to reproduce the transmittedintelligence, a common source of electrical current to supply energizingcurrent to said transmitting and receiving stations, an individual cablecon necting each of said receiving stations to said transmittingstation, each of said cables providing a transmission circuit for saidsource of electrical energizing current to the associated receivingstation and providing a transmission line terminated in itscharacteristic impedance for transmitting said electrical currents fromsaid transmitting station to the associated receiving station, aplurality of impedances each having a magnitude approximating thecharacteristic impedanoe of each of said transmission lines, andswitching means associated with each of said cables and operative in afirst condition of adjustment to disconnect said source of electricalenergizing current from both the transmitting and receiving stations andto connect one of said impedances to said transmitting station in lieuof the associated receiving station, operativein a second condition ofadjustment to maintain the last mentioned connection and to connect saidsource of electrical energizing current to both the transmitting andreceiving stations, and operative in a third condition of adjustment tomaintain the connection last mentioned and to connect the associatedreceiving station to the transmitting station in lieu of the said oneimpedance.

3. Apparatus for selectively transmitting intelligence to one or more ofa plurality of receiving stations from a transmitting station includingmeans at said transmitting station to produce electrical currentsrepresentative of the .intelligence to be transmitted, reproducingmechanism at each of said receiving stations and responsive to acharacteristic of said electrical currents to reproduce the transmittedintelligence, means to vary the response of said reproducing mechanismto changes in said characteristic of said electrical currents, a commonsource of electrical current to supply energizing current to saidtransmitting and receiving stations, an individual cable connecting eachof said receiving stations to said transmitting station, each of saidcables providing a transmission circuit for said source of electricalenergizing current to the associated receiving station and providing atransmission circuit path for said electrical currents from saidtransmitting station to the associated receiving station, a plurality ofimpedances each having a magnitude approximating the input impedance ofeach of said transmission circuit paths, and switching means associatedwith each of said cables and operative in a first condition ofadjustment to disconnect said source of electrical energizing currentfrom both the transmitting and receiving stations and to connect one ofsaid impedances to said transmitting station in lieu of the associatedreceiving station, operative in a second condition of adjustment tomaintain the last mentioned connection and to connect said source ofelectrical energizing current to both the transmitting and receivingstations, and operative in a third condition of adjustment to maintainthe connection last mentioned and to connect the associated receivingstation to the transmitting station in lieu of the said one impedance.

4. Apparatus for transmitting intelligence including means to produceelectrical signals of predetermined frequencies representative of theintelligence to be transmitted, a reproducing element, a voltageproducing frequency variation response network on which said electricalsignals are applied, said network including a primary circuit and atunable secondary resonant circuit reactively coupled to said primarycircuit, means responsive to the output voltage derived from saidnetwork to vary the tuning of said tunable secondary circuit and toadjust said reproducing element to reproduce the transmittedintelligence, and additional means to vary the tuning of said secondarycircuit to vary the response of said network to changes in thefrequencies of said signals.

RUDOLF F. WILD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,575,599 Hornberger Mar. 2, 19261,735,148 Weinberger Nov. 12, 1929 1,900,106 Hamilton et al Mar. 7, 19331,935,750 Singer Nov. 21, 1933 2,094,681 Sears Oct. 5, 1937 2,159,413Weinberger May 23, 1939 2,217,497 Shaw Oct. 8, 1940 2,274,638 RoseneMar. 3, 1942 2,330,109 Brown Sept. 21, 1943 2,380,982 Mitchell Aug. 7,1945 2,393,971 Busignies Feb. 5, 1946 2,396,091 De Bey Mar. 4, 19462,415,718 Wilson et al Feb. 11, 1947 2,446,392 Rey Aug. 3, 19482,474,527 Heisner June 28, 1949 OTHER REFERENCES CommunicationEngineering, Everitt, McGraw- Hill Book Co., Inc., 1937 (Chapters II andVIII).

